1. Are there two types of stem cells and embryonic stem cells and adult stem cells?2. What is the difference and when do they change from embryonic to adult? Upon birth?3. Is it only stem cells that differentiate or are there other types of unspecialised cells?4. When would a cell differentiate? Surely if someone loses lots of liver cells for example mitosis will replicate them rather than new ones through differnentiation?

1) yes, embryonic and from adult (although I don't think they are called adult stem cells)2) yes, the difference is the origin. Plus I think the ESC are the only really able to differentiate into any cell type. I'm not so sure about those from adults.

Adult stem cellsAlso known as progenitor cells or somatic stem cells, adult stem cells are located, in small quantities, throughout the body and generate specialized cells for the area they are located. These cells do not renew themselves as well as embryonic stem cells. Still, if these cells are put in a different environment, they may produce a different type of cells from the originating cell.

The key to stem cell differentiation is as Mark Holland pointed out.."put them in a different ENVIRONMENT and get a different outcome". Stem cells differentiate into cell-types relative to their SPECTRAL ENVIRONMENT. (Relative to the quanta frequency/frequencies they receive at that specific locus). Shine a specific low level (~5J/cm/cm) coherent light energy frequency at a stem cell and it will turn into the cell-type specific for that particular frequency.